PROJECT SUMMARY/ABSTRACT Extensive studies have indicated that post-translational modification by the small ubiquitin-like modifier (SUMO) family of proteins is a promising cancer therapeutic target. c-Myc-dependent cancers, including colorectal cancer, represent major unmet medical needs that currently lack targeted therapy. Recent scientific advances revealed that this ?undruggable? oncogene critically depends on SUMOylation. Furthermore, inhibiting SUMOylation can potentially activate anti-tumor immune responses. Genome-wide gene expression analysis of patient tumor tissues in comparison with normal tissues demonstrated that the SUMO activating enzyme (E1) is the most overexpressed SUMOylation-related protein in colorectal cancers tissues. SUMO E1 overexpression is also associated with cancer cell stemness and poor patient survival. This evidence makes SUMO E1 an attractive cancer therapeutic target. Therefore, our objective in this proposal to develop highly selective, potent, orally available and in vivo efficacious SUMO E1 inhibitors as targeted therapies for colorectal cancers that overexpress c-Myc. Using a fragment-based approach designed to target a newly discovered SUMO E1 allosteric binding site, we identified a class of potent and specific SUMO E1 inhibitors suitable for development into orally available drugs, which could represent a new class of therapeutic agents. In the proposed study, we will conduct lead optimization of these compounds and validate the resulting candidates in assays using colorectal cancer cell lines. To identify efficacious candidates with favorable bioavailability and pharmacokinetic properties, we will perform bioavailability, pharmacokinetic, and toxicity studies in mouse models. We expect to obtain a SUMO E1 inhibitor that is orally available and suitably potent in mouse models for further development. In addition to colorectal cancer, which is the focus of this proposal, inhibiting SUMOylation will likely inhibit other c-Myc-dependent cancers and potentially induce anti-tumor immune response. Thus, we expect the potent SUMO E1 inhibitors we develop in the proposed study to have a major impact on cancer research and targeted therapy.